Compositions containing vulcanizable silicon terminated organic polymers are well known in the art, and are commonly used as adhesives and/or sealants. For example, U.S. Pat. No. 3,632,557, incorporated herein by reference, describes room temperature curable silicon terminated organic polymers made by the reaction of an isocyanate terminated polyurethane prepolymer having urethane linkages and an organic silicon compound. Such polymers are commonly referred to as silylated polymers, and find use as adhesives and sealants, particularly in the automobile industry. Other patents relating to silylated polymers include U.S. Pat. Nos. 3,979,344; 4,222,925; 4,889,903; 4,894,426; 4,954,598 and 5,097,053, all incorporated herein by reference.
It is often desirable to provide such silylated polymer adhesive/sealant compositions in packages suitable for direct application of the product. A popular, efficient and economical type of package is an aluminum or aluminum-lined cartridge. Unfortunately, it has been discovered that such adhesive/sealant compositions often react with the aluminum, and corrode through the sides of such cartridges. Once the composition corrodes through the cartridge and is exposed to moisture in air, the curing process begins, and the adhesive/sealant solidifies before it can be used.
In using such adhesives and/or sealants, there are two important cure rates which need to be considered. The first is the surface cure rate, generally expressed as the tack-free time, that is, the time until the surface cures to the point of not being tacky. Generally, the application of the composition must be completed before such surface curing is complete. Therefore, the shorter the tack-free time, the less time one has to work with the adhesive/sealant. The second important cure rate is the cure-through rate. This is a measure of the time which it takes for the composition to cure through its thickness. The shorter the cure-through time, the sooner the finished product can be used. Therefore, it is often desirable to speed up the cure through rate of an adhesive/sealant while maintaining or even increasing the tack free time.
The present inventors made the discovery that methanol, which is commonly used in formulations of such adhesive/sealant compositions, reacts with aluminum when in the presence of the catalysts which normally are also included in such compositions. In an attempt to overcome the corrosion problem, the present inventors tested compositions prepared without methanol. Such compositions were found to be non-reactive with aluminum, and therefore to have a much longer shelf life in aluminum cartridges. Unfortunately, it was also found that the cure-through rate of silylated polymer adhesives and/or sealants without methanol was significantly slower than that of such adhesives/sealants with methanol. Increasing the amount of catalysts and using different catalyst systems did not improve the cure-through rate. In some cases, adding additional catalyst or using alternate catalysts was found to decrease the tack-free time significantly, thus making the adhesive/sealant more difficult to handle, but without improving the cure-through rate. Thus, there is a need for a methanol-free silylated polymer adhesive/sealant composition which is non-corrosive to aluminum with at least as fast a cure-through rate as compositions containing methanol.